OLED Pixel Compensation Circuitry for Hysteresis Error Elimination
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Solution Overview
Problem
Organic light-emitting diode (OLED) display pixels face challenges due to variations in transistor threshold voltages caused by process, voltage, and temperature (PVT) variations, leading to inconsistent light production and requiring compensation schemes that increase image display time.
Innovation Solution
Incorporating compensation circuitry that measures and compares sensing current from the drive transistor to apply external compensation, and using an anode reset transistor to maintain a constant voltage during pixel conditioning and current sensing operations, thereby eliminating hysteresis-induced current sensing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compensation schemes are used to compensate for transistor threshold voltage variations, then display pixel light production consistency is improved, but image display time increases
Solution Approach 1:
The patent performs current sensing operations during pixel conditioning operations, before the actual display operations. By measuring the sensing current and determining compensation values during the conditioning phase, the system prepares compensation data in advance. This preliminary action allows the display operations to proceed without additional time overhead, as the compensation values are already calculated and ready for application.
2Measurement precision
If current sensing operations are performed during pixel conditioning operations, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the pixel circuit components serve multiple functions. The drive transistor and associated circuit elements are used both for driving the OLED during display operations and for sensing current during conditioning operations. By configuring these existing components to perform dual roles, the patent achieves accurate current sensing without adding separate dedicated sensing circuitry, thus avoiding increased device complexity while maintaining measurement precision.
3Adaptability or versatility
If hysteresis effects are present during voltage transitions, then transistor operation flexibility is improved, but current sensing accuracy deteriorates
Solution Approach 1:
The patent applies preliminary anti-action by establishing a known reference voltage at the source terminal of the drive transistor before performing current sensing measurements. By pre-setting this reference voltage level during pixel conditioning, the system creates a stable baseline that counteracts hysteresis effects. This preliminary voltage establishment ensures that subsequent current measurements are taken from a consistent starting point, eliminating hysteresis-induced measurement errors while preserving transistor operation flexibility during actual display operations.
Data Source
AI summary
A display may include an array of organic light-emitting diode display pixels having transistors characterized by threshold voltages subject to transistor variations. Compensation circuitry may be used to sense a current from selected display pixels. A display pixel may include a drive transistor, a gate setting transistor for driving a reference voltage onto the gate terminal of the drive transistor, a data loading and current sensing transistor for connecting the drive transistor to a data/current-sensing line, a light-emitting diode, an emission control transistor coupled between the drive transistor and the diode, and an anode resetting transistor for selectively resetting the anode terminal of the diode. During pixel conditioning and current sensing operations, the anode resetting transistor may be constantly turned on to ensure that there is no voltage perturbation at the source terminal of the drive transistor, which can help prevent hysteresis-induced current sensing error.